1. Field of the Invention
The present invention relates to vehicle window glass and antennas that include a conductive film in which a slot is formed.
2. Description of the Related Art
Vehicle window glass of laminated glass formed by inserting an intermediate film between two glass plates inside which a conductive film is formed in order to reflect heat is known. In the case where an antenna conductor for receiving radio waves is formed on such vehicle window glass on its vehicle interior side, radio waves arriving frost outside the vehicle are blocked by the conductive film, so that the reception characteristics required of the antenna conductor may not be sufficiently obtained.
Window glass that uses a conductive film to have an antenna function in order to eliminate such an adverse effect is known. (For example, see Patent Documents 1, 2, 3, 4 and 5.)
Patent Documents 1, 2 and 4 are directed to slot antennas that use a slot between a flange of a vehicle body to which a glass plate is fixed and a conductive film. In the case of slot antennas that use a slot between a flange or a vehicle body and a conductive film, the size of the slot is determined vehicle type by vehicle type, and in particular, it is difficult to cause resonance at a predetermined frequency to receive radio waves in high-frequency bands. Furthermore, in order to receive radio waves in high-frequency bands, the positional relationship between the flange and the conductive film should be accurately controlled. However, there are variations in individual glass plates, and the glass plate is fixed to the flange of the vehicle body with an adhesive agent. Therefore, errors are variably caused in the thickness of the adhesive agent, the position at which the glass plate is fixed to the flange, etc. Accordingly, there has been a problem in that it as difficult to form slots of the same size in mass production.
Furthermore, in the case where a slot is provided in the conductive film in addition to the slot between the flange of the vehicle body and the conductive film as in Paten Document 4, the slot reduces the effect of the conductive film if the slot is large, and there is another problem in that a large heat distribution is generated on the glass plate based on the presence or absence of the conductive film so as to reduce forming accuracy when heating and bending the glass plate.
In order to solve the above-described problems, the antenna disclosed in Patent Document 5 is configured so that a slot formed in a conductive film is positioned between a pair of electrodes when the pair of electrodes is projected onto the conductive film and that the pair of electrodes and the conductive film are capacitively coupled. According to such an antenna configuration, a change in an external environment (including window glass, a part of a vehicle body to which window glass is attached, such as a flange, and the size and shape of a conductive film) is leas likely to change antenna characteristics.
[Prior Art Documents]
[Patent Documents]
[Patent Document 1] Japanese Laid-Open Patent Application No. 6-45817
[Patent Document 2] Japanese Laid-Open Patent Application No. 9-175166
[Patent Document 3] Japanese Laid-Open Patent Application No. 2000-59123
[Patent Document 4] United States Patent No. 5012255
[Patent Document 5] International Publication Pamphlet No. WO 2011/004877